Myosin Mg-ATPase of molluscan muscles is slightly activated by F-actin under catch state in vitro

Abstract

Molluscan muscle twitchin, a titin/connectin-related giant protein, regulates interactions between actin and myosin filaments at low Ca(2+) concentrations. When it is dephosphorylated, actin filaments tightly bind to myosin filaments, resulting in the catch state known as the state of high passive tension with very low energy consumption. Yet when twitchin is phosphorylated actin filaments detach from the myosin filaments, resulting in relaxation of the catch. Here, steady-state Mg-ATPase activities of purified myosin were measured under various conditions: without twitchin, with dephosphorylated twitchin, or with phosphorylated twitchin; with or without phalloidin-stabilized F-actin; and at various Ca(2+) concentrations. At low Ca(2+) concentration, Mg-ATPase was activated by F-actin only in the presence of dephosphorylated twitchin (catch state). The activation was about two orders lower than that fully activated by Ca(2+) and F-actin. In the absence of F-actin, twitchin and its phosphorylation state did not affect Mg-ATPase activities in any of the conditions we tested. Based on these results, we propose a molecular mechanism for the catch, where twitchin alone does not interact with the myosin catalytic motor domain but its complex with F-actin does, forming the bridge between actin and myosin filaments and the myosin slowly hydrolyzes Mg-ATP in the catch state.

Proteome changes in muscles, ganglia, and gills in Corbicula fluminea clams exposed to crude oil: Relationship with behavioural disturbances

“…Indeed, in exposed clams, there was an increase in valve closing duration and thus an increase in the catch mechanism. In bivalves, catch is a passive state of the smooth muscle that allow valves to remain closed for long periods with minimal energy consumption (Galler, 2008;Yamada et al, 2013). The valve opening amplitude was also lower, which is consistent with the decline in valve activity.…”

Differences between fast and slow muscles in scallops revealed through proteomics and transcriptomics

“…Over the past decades, extensive work has been done on invertebrate muscles, primarily in general structure of muscles, regulation of muscle contraction, and the mechanisms of contraction and motor function [ 9 – 13 ]. More recently, our knowledge of the unique physical properties of invertebrate muscles, has been reformulated with the advent of structural knowledge of thick and thin filaments [ 14 – 19 ], in vitro motility assay [ 20 , 21 ], and new evidences on the catch mechanism [ 22 – 25 ]. Recent work on fast and slow skeletal muscles reveals the complex regulatory mechanisms in key components of muscle structure, including the transcriptional and posttranscriptional events [ 3 , 4 ].…”